You can go one further than that too if you want. I have in the past also used 'resolution work type' categories e.g. 'replaced disk', 'update AD for customer' etc.

These can be useful when you're trying to work out what skills you need most and also understand call lengths and so on.

Be warned though, you can get lured into having lots and lots of these codes and they end up frustrating the team and take quite a bit of administration if you define every type of activity, so keep them broad to begin with. Make sure you really need them first!

Here is what our team is using (high level). Like UJ posted, be warned you can have lots and lots of these codes. For instance under the Root Cause Category - Change, I have different sub-categories that give more detail. Just make sure the information you use is useful to your processes and company culture. Let me know if you need more information.